feat(orchestrator): slice 4 — consolidated per-host sidecar (#352)

The core consolidation win: one persistent sidecar per host, shared by
every bottle, instead of a sidecar bundle per bottle. Safe to share
because the attribution invariant (source IP + identity token) lets the
sidecar map each request to the right bottle.

  * orchestrator/sidecar.py — a backend-neutral `Sidecar` lifecycle
    contract (mirrors LaunchBroker) + a `DockerSidecar` impl. The defining
    behaviour is idempotent singleton: `ensure_running` starts the instance
    if absent and is a no-op if it's already up, so N launches never spawn
    N sidecars; `stop` is idempotent.
  * orchestrator/dockerutil.py — a shared `run_docker` helper; DockerBroker
    now uses it too (DRY with slice 3).
  * service.py — the Orchestrator holds an optional `Sidecar`, exposes
    `ensure_sidecar()` + `sidecar_status()`.
  * control_plane.py — `GET /sidecar` reports it; __main__ gains
    `--sidecar-image` and ensures the single sidecar on startup.

Tests: unit (docker mocked) — is_running, ensure idempotent (no-op when up,
starts when absent), failure raises, stop idempotent; Orchestrator sidecar
wiring/status; control-plane /sidecar; integration (gated) — ensure is a
real idempotent singleton (one container after two ensures), stop removes.
Full suite green (only pre-existing /bin/sleep errors); integration
verified locally against real docker.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01WBMWTEtQdJ4W5UrWuLHCck

bot_bottle/orchestrator/dockerutil.py

@@ -0,0 +1,19 @@
+"""Shared `docker` subprocess helper for the orchestrator's docker-backed
+components (the launch broker and the consolidated sidecar)."""
+
+from __future__ import annotations
+
+import subprocess
+
+
+def run_docker(argv: list[str]) -> subprocess.CompletedProcess[str]:
+    """Run a `docker` command, capturing stdout/stderr as text. Never raises
+    on a non-zero exit — callers inspect `returncode` / `stderr` so they can
+    stay fail-closed or tolerate idempotent no-ops (e.g. removing an
+    already-absent container)."""
+    return subprocess.run(
+        argv, stdout=subprocess.PIPE, stderr=subprocess.PIPE, text=True, check=False,
+    )
+
+
+__all__ = ["run_docker"]